Hitherto, a magnetic recording medium prepared by coating on a non-magnetic support a coating composition composed of a ferromagnetic substance of an acicular form, such as .gamma.-Fe.sub.2 O.sub.3, CrO.sub.2, etc., dispersed in a binder has been widely used for magnetic recording and reproduction.
However, recently, the improvement of recording density has been strongly desired for attaining a large capacity of recording and the miniaturization of recording devices and in order to obtain a magnetic recording medium suitable for high-density recording using a conventional acicular ferromagnetic powder, it is required to sufficiently reduce the maximum size of the acicular ferromagnetic powder far below the recording wavelength or the length of the recording bit. At present, an acicular magnetic powder having a size of about 0.3 .mu.m has already been practically used and the minimum recording wavelength of about 1 .mu.m has been obtained.
For obtaining a magnetic recording medium capable of performing far higher density recording, it is required to further reduce the size of an acicular magnetic powder. However, since in such a small-sized acicular magnetic powder, the diameter thereof becomes very fine as less than 100 .ANG. and the volume of the particle becomes very small as less than 10.sup.-17 cm.sup.3, there are problems in that the magnetic characteristics are reduced by heat disturbance and the surface effect and also a sufficient orientation is not obtained by the application of a magnetic field to the coated magnetic layer.
Recently, for eliminating the above-described disadvantages, a magnetic recording medium using a tubular hexagonal system ferrite having an axis of easy magnetization perpendicular to the plane thereof as the ferromagnetic substance has been developed (see, Japanese Patent Application (OPI) Nos. 6525/83, 6526/83, etc.). (The term "OPI" as used herein means an "unexamined published application".) However, since such a hexagonal ferrite is of tabular form and has an axis of easy magnetization perpendicular to the plane thereof, the ferrite shows high aggregating force among the particles, whereby it takes a long period of time to disperse the ferrite powder in a binder and also it is difficult to obtain a sufficient degree of dispersion. Furthermore, the output and C/N of the magnetic recording medium using such a hexagonal ferrite cannot be sufficiently improved owing to the above-described disadvantage.